Disc for a turbomolecular pump

ABSTRACT

A disc for a turbomolecular pump formed of a plurality of disc elements assembled in an axial direction and each having a support ring, a plurality of vanes supported on the support ring and inclined to a plane of the support ring, and a plurality of radially extending slots provided between the vanes, with the support rings of the disc elements forming the support ring of the disc, the vanes of the disc elements forming the disc vanes, and the radial slots provided between the vanes of the disc elements forming the radially extending slots between the disc vanes, and with the vanes of one of disc elements least partially covering the radially extending slots of an adjacent disc element.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to discs for turbomolecular pumps and including a support ring, a plurality of vanes supported on the support rings, inclined to a plane of the support disc, and forming a circle, and a plurality of radially extending slots provided between the vanes.

[0003] 2. Description of the Prior Art

[0004] A turbomolecular pump is formed of rotor and stator discs alternatively arranged one behind the other and having each a vane crown. The pumping effect is based on transmission of pulses by the vanes of rotor discs to molecules of a pumped gas in the pumping direction. Both essential pumping characteristics, the suction capacity and the pressure ratio, substantially depend on the rotational speed of the rotor discs. The suction capacity linearly depends o the rotational speed, whereas the pressure ratio depends exponentially on the rotational speed. In order to achieve an optimal pumping effect, the rotational speed of the rotor should be as high as possible. As a result, the vanes of the rotor discs have to meet very high requirements with respect to their geometry, mechanical strength, and stability.

[0005] A further prerequisite for obtaining optimal pump characteristics is a minimal thickness of the vanes. Moreover, in addition to providing a large passing cross-section, which increases the suction capacity, an important role is played by strength considerations taken into account in designing the vanes and in selecting the rotational speed. While striving for a high rotational speed, one must insure, at the same time, that a centrifugal force, which acts on the vanes, vane base, and inner diameter of the rotor disc, is kept at a minimum.

[0006] A further criterium of optimal pump characteristics is an optical density of separate discs. In increased optical density prevents axial backflow within the disc stack.

[0007] At present, essentially two types of discs for turbomolecular pumps are known. With one type, the discs are formed as massive discs with radially extending, inclined to the disc plane, vanes being milled out. With the other type, the discs are formed of sheet material, with the vanes being stamped out of the disc plane. The milled discs are formed of aluminum as this material is easily milled. However, in many cases in which the turbomolecular pumps are used, highly corrosive gases need to be pumped. As aluminum is not corrosion-resistant, the aluminum disc can be used in pumps operable in a corrosive environment. They can be used only if they are provided with a corrosion-resistant coating. This, however, substantially increases manufacturing costs.

[0008] On the other hand, high corrosion-resistant materials, such as alloyed steel, not particularly suitable for milling. However, the sheet metal can be stamped rather easily.

[0009] However, one of the main drawbacks of the discs made of sheet material with stamped and shaped vanes consists in that these discs are not optically dense. This leads to high backflow losses in a pump. A further drawback consists in that an entire mass of vanes of a disc is relatively big with respect to the radial surface of the support ring. This lead to large centrifugal forces acting on the supporting which limits the rotational speed of the pump and, thus, its output capacity.

[0010] Accordingly, an object of the present invention is to provide a turbomolecular pump disc which is formed of a corrosion-resistant material, can be cost-effectively produced, and is devoid of the above-discussed drawbacks.

[0011] Another object of the present invention is to proved a turbomolecular pump disc having a high optical density. A further object of the present invention is to provide a turbomolecular pump disc with which the load resulting from the action of the centrifugal forces is kept within acceptable limits while the pump operates with a maximal possible rotational speed.

SUMMARY OF THE INVENTION

[0012] These and other objects of the present invention, which will become apparent hereinafter, are achieved by providing a disc formed of a plurality of disc elements assembled in an axial direction and each having a support ring, a plurality of vanes supported on the support ring and inclined to a plane of the support ring, and a plurality of radially extending slots provided between the vanes, with where the support rings of the disc elements forming the support ring of the disc, the vanes of the disc elements forming the disc vanes, and the radially extending slots provided between the vanes of the disc elements forming the radially extending slots between the disc vanes, and with the vanes of one of the plurality of disc elements at least partially covering the radially extending slots of an adjacent disc element in the assembled condition of the disc.

[0013] The disc according to the present invention can be formed of corrosion-resistant materials, with the gas delivery structure being formed by stamping out of the radial slots and by stamping the vanes out of the disc plane, with subsequent appropriate shaping of the vanes. The assembly of the disc of several disc elements insures a high optical density of the disc, which prevents backflows both within the disc itself and within the entire disc stack. In addition, the disc elements can be formed with a reduced number of vanes than when a solid disc is formed, while obtaining the same optical density.

[0014] Because in the disc according to the present invention, the load, which is caused by the centrifugal force and acts on the vane case and the supporting, is reduced to a minimum, the pump can operate with a higher rotational speed which insures obtaining optimal pump characteristics. The advantage of the inventive disc also consists in that that the vanes can be made thinner than in a disc with milled out vanes, which permits to increase the passing cross-section of the pump, further improving the pump characteristics. Thinner vanes also contributes to the reduction of the centrifugal force acting on the vane base and the support disc.

[0015] The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to is construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiment, when read with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings show:

[0017]FIG. 1 an exploded view of a two-part rotor disc according to the present invention for a turbomolecular pump;

[0018]FIG. 2 a perspective view of the two-part rotor disc shorn in FIG. 1 in a semi-assembled condition; and

[0019]FIG. 3 a perspective view of the two-part rotor disc shown in FIG. 1 in an assembled condition.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0020] A rotor disc according to the present invention, which is shown in FIGS. 1-3, is formed of two disc elements 11 and 12. Each of the disc elements 11, 12 has a support ring 21, 22, respectively, and a plurality of vanes 31, 32 secured to the respective support ring 21, 22. The vanes 31, 32 are inclined to a plane of the respective disc elements 11, 12 and are so shaped that they form a gas delivery structure. A plurality of openings in a form of radially extending slots 41, 42 are provided between respective vanes 31, 32. The two disc elements 11, 12 are assembled together, forming a rotor disc shown in FIG. 3. A position of the two disc elements 11 and 12, in which they are already engaged in each other but are not yet fixedly connected with each other, is shown in FIG. 2. In FIG. 3, both disc elements 11, 12 are joined with each other with aid of joining clips 51, 52, forming a rotor disc 1. The two support rings 21, 22 form an inner support disc 2, and the vanes 31, 32 form rotor disc vanes 3 supported on the support ring 2 at an angle to the plane of the rotor disc 1, with radially extending slots 4 formed between the vanes 3. However, in the axial direction of the rotor disc 1, the vanes 3 form an optically impermeable surface. The disc elements 11-12 are formed as a sheet metal body, with the vanes 31-32 being formed by being stamped out of the disc element plane.

[0021] In the embodiment shown in the drawings, the rotor disc according to the present invention is formed of two disc elements. However, a rotor disc can be formed of more than two disc elements.

[0022] It is to be noted that stator disc of a turbomolecular pump can be formed in a similar manner. In this case, as a rule, the vanes are located radially within the support ring.

[0023] Through the present invention was shown and described with references to the preferred embodiment, such are merely illustrative of the present invention and are not to be construed as a limitation thereof, and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiment within the spirit and scope of the present invention as defined by the appended claims. 

What is claimed is:
 1. A disc for a turbomolecular pump, comprising a support ring; a plurality of vanes supported on the support rings, inclined to a plane of the support disc, and forming a circle; and a plurality of radially extending slots provided between the vanes, Wherein the disc is formed of a plurality of disc elements assembled in an axial direction and each having a support ring, a plurality of vanes supported on the support ring and inclined to a plane of the support ring, and a plurality of radially extending slots provided between the vanes, Wherein the support rings of the disc elements form the support ring of the disc, the vanes of the disc elements form the disc vanes, and the radially extending slots provided between the vanes of the disc elements form the radially extending slots between the disc vanes, and Wherein in the assembled condition of the disc, the vanes of one of the plurality of disc elements at least partially cover the radially extending slots of an adjacent disc element.
 2. A disc as set forth in claim 1, wherein the vanes of the disc elements forming an optically infermeable surface in the axial direction.
 3. A disc as set forth in claim 1, wherein the disc elements are formed as sheet metal body, with the vanes being stamped out of a disc element plane. 